Exemplary embodiments of the present invention relate to a waste heat utilization device for a motor vehicle having an internal combustion engine. Exemplary embodiments of the invention further relate to a motor vehicle having such a waste heat utilization device, and an operating method for a motor vehicle having such a waste heat utilization device.
A conventional waste heat utilization device, which preferably operates according to the Rankine cycle or according to the Clausius-Rankine cycle, usually includes a waste heat utilization circuit in which a working medium circulates. A conveying device for driving the working medium, an evaporator for evaporating the working medium, an expansion machine for expanding the working medium, and a condenser for condensing the working medium are successively situated in the waste heat utilization circuit in the direction of flow of the working medium.
German patent document DE 24 00 760 describes a motor vehicle that may be alternatively or simultaneously driven by an internal combustion engine and an electric motor.
U.S. Pat. No. 4,405,029 discloses a hybrid vehicle that includes an internal combustion engine and an electric motor. The electric motor may be operated by means of a waste heat utilization device. The electric motor may be used for driving a transmission as well as for charging a battery. The electrical energy stored in the battery may in turn be used, if necessary, for driving the electric motor.
European patent document EP 1 249 585 A1 discloses a heat exchanger of a multi-cylinder internal combustion engine. The heat exchanger may be designed as a waste heat utilization device that is mounted in a motor vehicle. The waste heat utilization device in turn includes an evaporator that generates steam at an elevated temperature and elevated pressure, wherein waste heat, such as exhaust gas of an internal combustion engine, is used as the heat source. A rotary shaft is driven by means of an expansion machine by expansion of the high-pressure steam, and the steam is re-condensed by means of a condenser. By means of the expansion device, an output shaft of an internal combustion engine as well as an electrical generator which may, for example, electrically charge an electrical energy store, in particular a rechargeable battery, may be driven via a mechanical coupling.
European patent document EP 1 326 017 A1 describes a Rankine circuit system for utilizing waste heat of an exhaust gas from a hybrid vehicle. The system includes an internal combustion engine as the drive source for the motor vehicle, and an electric generator motor. An output torque of the system is supplied to a transmission, and is used to provide an additional drive force for a drive train of the motor vehicle or to electrically charge a chargeable battery. During an acceleration of the motor vehicle, thermal energy of the exhaust gas is utilized by the system, and during a deceleration of the motor vehicle, the kinetic energy of the motor vehicle is converted to provide regenerative electrical power for the electric generator motor, so that the fuel consumption in the internal combustion engine may be reduced.
Exemplary embodiments of the present invention are directed to an improved design for a waste heat utilization device and for a motor vehicle using such a waste heat utilization device. Exemplary embodiments of the present invention are also directed to an improved operating method for such a motor vehicle.
The waste heat utilization device according to the invention includes a waste heat utilization circuit in which a working medium circulates. The waste heat utilization device includes a conveying device, situated in the waste heat utilization circuit, for driving the working medium, and an evaporator, situated in the waste heat utilization circuit downstream from the conveying device, for evaporating the working medium. Furthermore, the waste heat utilization device includes an expansion machine, situated in the waste heat utilization circuit downstream from the evaporator, for expanding the working medium, and a condenser, situated in the waste heat utilization circuit downstream from the expansion machine, for condensing the working medium.
For energy recovery, the expansion machine is now in direct drive connection with a power take-off shaft of the internal combustion engine. Output drive power of the internal combustion engine of the motor vehicle may be assisted in this way. In addition, as the result of providing an electrical generator that is in direct or indirect drive connection with the power take-off shaft, besides the above-mentioned direct energy recovery, the generation of electrical energy is also possible. The electrical energy generated in this way may be used in particular for driving an electric motor, via which in turn the drive of a main output shaft of the internal combustion engine may be assisted. Alternatively or additionally, however, it is also possible for the generated electrical energy to be temporarily stored in a suitable energy store, such as a chargeable battery. By means of the electrical energy that is temporarily stored in such a battery, an electric motor situated on a main output shaft of the internal combustion engine may then be driven, or, if the electrical generator is designed as a so-called generator motor, the electrical generator may be driven for operation as an electric motor by means of the electrical energy stored in the energy store, in order to likewise assist the drive power of the internal combustion engine via the power take-off shaft. The efficiency of the internal combustion engine may be significantly increased by means of a waste heat utilization device designed according to the invention as described above.
In one embodiment the expansion machine may have a rotor and a turbine wheel connected to the rotor in a rotationally fixed manner and drivable by the energy that is released during expansion of the working medium, wherein the power take-off shaft of the internal combustion engine is the rotor of the expansion machine. According to the invention, the term “direct drive connection” is thus understood to mean that the expansion machine is situated directly on the power take-off shaft of the internal combustion engine, so that the power take-off shaft simultaneously functions as a rotor of the expansion machine. A space-saving and technically simple, and therefore cost-effective, design of the waste heat utilization device according to the invention is thus possible.
In one embodiment, the electrical generator may be situated on the power take-off shaft. In that case, the expansion machine and the electrical generator are both placed on the power take-off shaft of the internal combustion engine, as the result of which the space requirements for the waste heat utilization device according to the invention may be further reduced.
Alternatively, however, it is possible to situate the electrical generator on a separate generator shaft that is in operative connection with the power take-off shaft. The electrical generator may thus be spatially separate from the expansion machine if this should be necessary for technical reasons, for example.
The power take-off shaft is then in drive connection with the generator shaft by means of a wheel drive, in particular a belt drive, chain drive, or gear drive. A torque of the power take-off shaft may thus be transmitted to the generator shaft of the electrical generator, which is spatially separate from the power take-off shaft, in a technically simple and space-saving manner. The wheel drive may also include a gear unit by means of which a certain gear ratio between a generator shaft of the electrical generator and the output shaft may be achieved. This embodiment as well allows a flexible and compact design of the waste heat utilization device.
In one particularly compact and therefore space-saving embodiment, the power take-off shaft may be led coaxially through the expansion machine in such a way that the electrical generator or the wheel drive is situated on a side of the expansion machine facing away from the internal combustion engine. Alternatively, the power take-off shaft may be led coaxially through the electrical generator or the wheel drive, so that the electrical generator or the wheel drive is situated on the power take-off shaft on a side of the expansion machine facing the internal combustion engine.
To be able to re-supply the electrical energy generated by the electrical generator to the drive train of the motor vehicle in order to increase the power, the waste heat utilization device may also include an electric motor which is drivable by the electrical generator. For this purpose, the electric motor may be in drive connection with a main output shaft of the internal combustion engine.
Alternatively or additionally, in one embodiment the electrical generator itself may be designed as a so-called generator motor, so that in a coasting mode state of the motor vehicle the generator motor may act as an electrical generator for generating electrical energy, and in a drive mode state of the motor vehicle may act as an electric motor for driving the power take-off shaft of the motor vehicle. Thus, in the drive mode state, additional drive power may be supplied to the drive train of the motor vehicle in the manner of a so-called “booster,” via the main output shaft (by means of a separate electric motor) or via the power take-off shaft (by means of the electrical generator which is designed as a generator motor). The energy necessary for operating the electric motor or generator motor may be withdrawn from a suitable electrical energy store, such as a chargeable battery. The charging of this electrical energy store may then take place by means of the electrical generator, for example when the motor vehicle is in a coasting mode state. In such an operating state, the motor vehicle is not accelerated or even decelerated, so that the electrical energy generated by the electrical generator is not needed by the drive train of the motor vehicle, and instead may be temporarily stored in the electrical energy store for later use.
Furthermore, in one embodiment the electrical generator may be designed in such a way that it is switchable for selectively charging the electrical energy store, in particular the battery, or for driving the main output shaft. The electrical energy generated by the electrical generator may thus be reused in an energy-efficient manner.
The invention further relates to a motor vehicle having an internal combustion engine which includes a main output shaft and a power-take off shaft, and having a waste heat utilization device with one or more of the above-mentioned features. The invention further relates to a method for operating a motor vehicle having this type of design.
Further important features and advantages of the invention result from the drawings, and the associated description of the figures with reference to the drawings.
It is understood that the features mentioned above and to be explained below are usable not only in the particular stated combination, but also in other combinations or alone without departing from the scope of the present invention.